In tape automated bonding (TAB) packaging technology, a set of beam leads (a "lead frame") electrically interconnects a semiconductor chip to a wiring substrate, for instance, a printed circuit board. The beam leads are supported on a polymer substrate and the combination is called a TAB tape. Each frame of the TAB tape contains a new set of beam leads.
Each lead frame further includes an inner lead bond area where individual beam leads are aligned with a chip's contact locations, and an outer lead bond area for electrically interconnecting the chip to a substrate. A heated bonding head ("thermode") is brought into contact with the inner lead bond area and presses the individual beam leads against the chip's contacts to thermally compression-bond them.
TAB tapes generally are provided with sprocket holes whose purposes is to enable the feeding of the tape during chip placement and bonding. The sprocket holes usually have a form that is familiar from movie films and thus, prior art mechanisms used for transporting movie films have been used to transport TAB tapes. However, as TAB technology has moved in the direction of more leads and smaller spacings, such transport mechanisms have been found inadequate. When lead counts were low and lead widths were large, mechanical alignment using the sprocket holes was satisfactory. However, lead sizes today are on the order of two mil widths on four mil centers, and prior art sprocket positioning techniques are no longer adequate.
As a result, the semiconductor industry now employs optical alignment techniques (e.g., pattern recognition using solid state imaging cameras) to provide vernier positioning signals to enable precise location of chips on TAB lead frames. Precise mechanical alignment devices and thus joined with the optical system to enable the mechanical motion adjustments to be achieved.
A known mechanism for feeding strip materials is known as the hitch feeder. A hitch feeder usually includes a pneumatically operated slide, adjustable mechanical stops to control the stroke of the slide; grippers to grip the strip material that is attached to the slide; another gripper that is fixed in space that also grips the material; and a means for actuating the slide and grippers in a particular order. The hitch feeder propels material forward by gripping it with grippers attached to the slide and then actuating the slide.
The mechanical motion of the slide pulls material along, and when the slide reaches the end of its stroke, the gripper that is fixed in space grabs the material and the movable gripper is released. The slide is then actuated in the reverse direction and returns to its starting point. The material thus only travels on the forward stroke of the slide.
Examples of hitch feeders may be found in U.S. Pat. No. 3,753,522 to Voges; 3,791,567 to Schott Jr.; and 4,218,004 to Rouse. Each of the aforementioned patents employs hitch feed devices for moving flexible webs. In each instance however, there is no requirement to register the web material with any other apparatus, nor to worry about conductors or other materials adhering to the surface of the web. Thus, each employs a gripping mechanism which, on the return stroke, enables one of the jaws of the gripping mechanism to be in contact with the web material. In U.S. Pat. No. 4,851,902 to Tezuka et al. an individual lead frame feed system is described which has vernier positioning provisions for the lead frames. Neither hitch feeding nor the handling of a continuous TAB tape is considered. Other references relevant to this technology are U.S. Pat. Nos. 4,194,673 to Elbert et al. and 3,937,388 to Zimmerman.
Accordingly, it is an object of this invention to provide a hitch feeder which enables precise alignment of features on a web.
It is another object of this invention to provide an improved hitch feeder which enables vernier adjustments to the position of the web, as it is being hitch fed.
It is a further object of this invention to provide an improved hitch feeder for handling TAB tapes.
It is yet another object of this invention to provide a hitch feeder for TAB tape which moves the tape without contact being made to circuit features on the tape.